Rechargeable alkaline manganese cell with cathode consistency compensation

Abstract

In an improved rechargeable alkaline manganese cell that has a manganese dioxide cathode comprising pellets formed by pressing a cathode powder blend comprising a hygroscopic additive for increasing cumulative capacity, the sticky consistency of the pellets, which is un-desirable for continuous automated production is compensated for by the addition of up to 0.5% of a hydrophobic binder. This small amount leaves the cell performance substantially unimpaired, but provides the desired consistency for large-scale production. Further disclosed is an improved charge methodology for a rechargeable alkaline manganese cell wherein the charge current is pulsed at a voltage in excess of 1.65 V and the no-load cell voltage response is monitored at predetermined intervals. No charge current pulse is permitted to pass through the cell if the no-load voltage exceeds a threshold value. This results in increased utilization of the capacity of the cell while reducing the likelihood of damage to the cell due to overcharging.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. patent application 60 / 537,900, filed Jan. 22, 2004.FIELD OF THE INVENTION [0002] The invention relates to rechargeable alkaline batteries. Specifically, the invention relates to cathode formulations of such batteries that comprise a hydrophobic cathode additive for affecting the consistency of pressed cathode pellets to make them more amenable to continuous production. The invention also relates to an improved charging method for use with rechargeable alkaline manganese cells, particularly the cells of the present invention. BACKGROUND OF THE INVENTION [0003] Alkaline battery technology has been used since the 1970's to provide inexpensive, long-lasting portable power sources for a variety of electrical applications. Disposable alkaline batteries, or primary cells are the most common example. However, due to recent technical advancements, re-chargeable alkaline batteries, or secondary cells, h...

AI Technical Summary

Benefits of technology

[0014] The present invention advantageously provides a cathode with an acceptable consistency when pressed and formed into a cathode pellet, without noticeably decreasing the electrical performance of the cells made using the pellet.

[0019] The charge methodology of the present invention advantageously results in increased charging efficiency and cumulative cell capacity of rechargeable alkaline cells in a safe and automatable manner. Approximately a 15% increase in cell capacity may be obtained. A current pulse may be permitted to pass through the cell only if the no-load voltage does not exceed the first charge voltage to prevent damage to the cell through overcharging. The first charge voltage may be 1.75 V. The current pulse may have a duration of 14.5 seconds. The pre-determined time interval may be 0.5 seconds.

Problems solved by technology

Without the addition of sufficient binder (typically about 1.0-2.0% by weight) excessive pellet breakage occurs during automated production.

The addition of a binder has an adverse impact on cell performance; since binders are electrochemically inactive, the presence of the binder reduces the quantity of active cathode components, such as manganese dioxide, that are available to participate in electrochemical reactions.

Also, binders are typically non-conductive.

Lower concentration is not effective in achieving the aforementioned advantages.

The addition of a binder to these cells is undesirable, since the presence of the binder reduces cell performance.

In fact, when barium compounds such as BaO or Ba(OH)2*8H2O are used as additives, the formed pellets exhibit a “sticky” consistency that impedes continuous processing.

As a result, the improved cathode formulations cannot be used in a continuous production environment, making batteries with these formulations too expensive for the end-user.

Although binders are used to increase flexural strength of the cathode as an aid in continuous pellet processing, binders are not normally selected to modify the consistency of the cathode pellet.

Rechargeable alkaline cells are prone to cell failures when overcharging takes place.

Overcharge results in damage to cell components and will cause increased internal gassing, which in turn may eventually cause the cell to fail from electrolyte leakage due to overpressure.

However, a portion of the cell's capacity is not re-charged, which results in a loss of available performance.

The loss of available performance is especially significant when inert materials such as additives or binders are added to the cathode, as the presence of these materials reduces the amount of active cathode component available for electrochemical reaction.